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. 2017 Feb 6:8:14353.
doi: 10.1038/ncomms14353.

Photo-driven redox-neutral decarboxylative carbon-hydrogen trifluoromethylation of (hetero)arenes with trifluoroacetic acid

Jin Lin  1 , Zhi Li  2 , Jian Kan  1 , Shijun Huang  1 , Weiping Su  1 , Yadong Li  2
Affiliations

Photo-driven redox-neutral decarboxylative carbon-hydrogen trifluoromethylation of (hetero)arenes with trifluoroacetic acid

Jin Lin et al. Nat Commun. .

Abstract

Catalytic oxidative C-H bond functionalization reactions that proceed without requiring stoichiometric amounts of external oxidants or pre-functionalized oxidizing reagents could maximize the atom- and step-economy in chemical syntheses. However, such a transformation remains elusive. Here, we report that a photo-driven catalytic process enables decarboxylative C-H trifluoromethylation of (hetero)arenes with trifluoroacetic acid as a trifluoromethyl source in good yields in the presence of an external oxidant in far lower than stoichiometric amounts (for example, 0.2 equivalents of Na2S2O8) using Rh-modified TiO2 nanoparticles as a photocatalyst, in which H2 release is an important driving force for the reaction. Our findings not only provide an approach to accessing valuable decarboxylative C-H trifluoromethylations via activation of abundant but inert trifluoroacetic acid towards oxidative decarboxylation and trifluoromethyl radical formation, but also demonstrate that a photo-driven catalytic process is a promising way to achieve external oxidant-free C-H functionalization reactions.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Catalytic oxidative C–H functionalization.
(a) Minisci reaction: the example of the C–H functionalization with stoichiometric external oxidant. (b) C–H trifluoromethylation with Umemoto reagent: the example of C–H functionalization with pre-synthesized oxidazing reagent. (c) Photo-driven C–H trifluoromethylation without the reliance on external oxidant (this work).
Figure 2
Figure 2. Photo-driven C–H trifluoromethylation of substituted benzenes and nitrogen-containing heteroarenes.
Standard reaction conditions: substrates (0.5 mmol), 0.1 wt% Rh/anatase TiO2 NPs (20 mol%), Na2S2O8 (10-40 mol%), TFA (10–15 ml), 365 nm ultraviolet, room temperature, 24 h. Yields were determined by 19F NMR spectrum. †Isolated yield.
Figure 3
Figure 3. Mechanism studies.
(a) Synthesis of CF3I via decarboxylative coupling of I2 with TFA. (b) Capture of CF3 radical by TEMPO. (c) Determination of CF3H and C2F6 side products in trifluoromethylation of caffeine. (d) Determination of H2 and CO2 from the photo-driven decarboxylation of TFA. (e) The proposed reaction mechanism.
Figure 4
Figure 4. Characterization of the nanocatalyst.
(a) TEM image of Rh/TiO2 (scale bar, 50 nm), (b) HRTEM image (scale bar, 5 nm) and lattice fringe image (inset, scale bar of 2 nm) of Rh(0) NP. HRTEM, high-resolution TEM.
See this image and copyright information in PMC

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